The basic aircraft propeller has in the past been made of structural materials that have fallen short of their expected potential because of an increase in only one of the important structural efficiency parameters such as strength or stiffness. These materials have included steel, wood, aluminum, titanium, and the like. Because of these deficiencies, the aircraft industry has taken an intense interest in advanced fibrous reinforced composites. Proper use of these materials offers greater strength while reducing the weight structure of a blade by as much as fifty percent.
The aircraft blade contemplated in this invention is included in a counterrotating propeller system having a fore propeller with five to fifteen blades and a counterrotating aft propeller with from five to fifteen blades. The blades are highly swept, wide chord and very thin. The airfoils of the propeller blades operate at transonic and supersonic speeds.
Previous propeller blade designs were adequate for subsonic flight. However, numerous structural problems causing decreased performance resulted when these blades were used at high subsonic flight. The structural problems for a blade operating at a very high speed resulted from the forces and stresses acting on the blade. The forces acting on a blade in flight are thrust, centrifugal force, and torsion forces. First, the thrust induces bending stress in the blade. Second, the centrifugal force stretches the blade in the radial direction. Finally, the torsion forces the blade to twist about the radial axis of the blade. The ideal blade overcomes these forces while minimizing weight for efficient fuel consumption.
A solution to the blade problem has been the development of fiber reinforced resin-bonded structural composite materials. These materials have created a new design flexibility for propellers. There are three major advantages to the application of fiber reinforced composites. First, complex airfoil configurations can be shaped. Second, composite materials create weight savings. Third, the dynamic frequency response of the blade element can be tailored to its operating parameters. This invention overcomes the problems and disadvantages of the prior art blades by providing a propeller blade comprised of composite materials having the strength and airfoil configuration to provide an efficient blade for a counterrotating propeller system.